Hollow pile driving mandrel



2 SheetsSheet 1 Filed Nov. 15, 1963 FIG. 2

INVENTOR. FREDRIC RUSCHE ATTORNEY Aug. 30, 1966 F RUSCHE HOLLOW FILE DRIVING MANDREL 2 Sheets-Sheet 2 Filed Nov. 15, 1963 .IIINIIIIIII.

FIG. 4

CHANNELS WELDED INSIDE TUBE TUBES WELDED END TO END 5 IIIID I II" IEIIIIII INVENTOR.

FREDRIC' RUSCHE BY v WM CHANNELS WELDED TO 6 TUBE 8 TO EACH OTHER INSIDE United States Patent 3,269,127 HULLOW FILE DRIVING MANDREL Fredric Rusche, Southfield, Mich. (8125 Medina 81L, Detroit, Mich.) Filed Nov. 15, 1963, Ser. No. 323,941 12 Claims. (\Cl. 61-5372) This invention relates to pile driving mandrels of the type disclosed in my US. Patent 3,006,152, issued October 31, 1961, the disclosure of which is incorporated herein by reference.

In pile driving operations it is customary to drive into the ground a stout tubular mandrel surrounded by a thin, relatively delicate casing which casing is to form a mold of a concrete pile. The piles may be of the order of a foot in diameter and may be required to be from about 10 feet to about 80 feet long. The casings are made of thin steel for example of 16 gauge. They may be corrugated spirally as known in the art and as shown for example in the US. patent to McKee 2,928,252. The assembly of mandrel and easing punches a hole in the earth after which the mandrel is removed, leaving the casing in the hole to form a permanent mold for pouring the concrete pile.

It is of advantage to drive such casings with a solid core mandrel, by which I mean a mandrel, the driving member of which is a circumferentially integral or complete tube which is not split nor made in longitudinal sections. Such solid core mandrels as disclosed in my patent referred to, have been very successful in driving casings but various problems have been encountered which the present invention is intended to solve.

In mandrels of this type the great force of the driving hammer must be transmitted to the thin shell through expressable and retractable connections between the mandrels and the shells. Such connections are shown in that patent in the form of long lines of plugs extending the length of the mandrel. Each plug is movable radially in an opening through the wall of the tubular mandrel to engage and interlock with the corrugations of the shell and thus form a driving connection between the mandrel and the shell. Expansible, flexible fluid pressure chambers formed by hoses or bladders filled with air under pressure are used to express the plugs into contact with the shells, and springs are used to retract the plugs when the air pressure is relieved.

Two forms of plugs and springs have been proposed. In the forms shown in FIGS. 4 and 5 of my patent referred to, circular plugs are placed in circular holes through the wall of the mandrel and these are retracted by a coil spring surrounding each plug inside of the hole. This arrangement requires retaining rings for the springs and clearance between the plug and the hole in which the springs may be placed. This in turn requires all of the force of the driving hammer to be transmitted through the retaining rings. Such structure limits the amount of driving force that can be transmitted without damaging or destroying the force transmitting devices.

Accordingly it has been proposed to make the driving connections or plugs in the form shown in FIGS. 9 through 12 in which a stout elongated plug bears directly against the wall of the hole through which it slides and transmits the force of the hammer on the tube edgewise through the elongated plug to the shell. This permits direct driving contact between the Wall of the tube which may be of the order of an inch and a quarter thick and permits the use of a plug having a cross section as long as desired, for example of the order of 14 inches. Such a plug, in direct contact with the thick wall of the tube through which it passes, can transmit a very great force without damage to the plug. The length of the plug permits corrugations in its surface or lugs on its surface to match a large number of corrugations in. the tube. This can successfully transmit great force to the shell.

While the plugs as just described are successful in transmitting great driving forces to the shell problems arise in connection with the expressing and retracting of the plugs.

As previously proposed the long line of plugs, running the length of the mandrel (which may be as much as 60 feet) is mounted on a single steel channel member running the length of the mandrel. This channel member is pushed radially outward by a hose running the length of the mandrel and filled with air under pressure. The plugs are retracted by pushing the channel radially inward by a number of separate coil springs distributed along the length of the channel, the channel being bolted to all the plugs in one row. This arrangement requires a large number of springs which must be inserted in a large number of holes drilled through the wall of the tube and tapped to receive backing plugs or spring abutments threaded into these holes.

This arrangement has proved inconvenient and expen sive. The tubes forming the mandrel are of hard steel through which it is diflicult and expensive to bore and tap a large number of holes. On the other hand the elongated openings which support the plugs can be readily and cheaply formed by a cutting torch.

Another problem arises from the existence of the four elongated channels and the necessity of supporting four elongated hoses running the length of the mandrel, keeping them accurately in contact with the channels, and supplying them with air under pressure. This has required an elaborate, heavy and extensive steel structure, known as guts, which is placed inside of the mandrel tube and runs its entire length. Because of the necessity of having this structure run the entire length of the mandrel it has been impossible to weld the structure to the mandrel tube throughout its length. This has resulted in floating guts, that is guts separated structurally from the mandrel. The large inertia of the guts causes great reaction force on the tube and on the hose connections when the hammer strikes the tube. The tube tends to sink into the earth under the force of the hammer and the guts tend to remain in place. This causes bending or whipping of the guts, vibration, rupture of the air pressure connection to the hoses, and other disadvantages.

It is among the objects of the present invention to provide an improved mandrel of the general type illustrated in my patent referred to and to eliminate the problems arising from floating guts, while providing improved supports or containers for the hoses which supports run the length of the mandrel and are secured to the wall of the mandrel throughout their entire length.

It is another object of the invention to provide an improved arrangement for retracting the plugs which do not require separate openings for the mounting of springs.

It is another object of the invention to provide an improved arrangement of air connections to the hoses which is not subject to damage or disruption by vibration or inertia forces.

These and other objects and advantages of the invention will be apparent from the following description and accompanying drawings, in which the same reference character always designates the same part wherever it occurs.

In the drawings:

FIG. 1 is a view partly in elevation and partly in section of a mandrel embodying one form of the invention,

FIG. 2 is a section on an enlarged scale on the lines 22 of FIG. 1,

FIG. 3 is a section on a correspondingly enlarged scale on the line 33 of FIG. 1,

FIG. 4 is a diagrammatic section of a portion of a mandrel showing a step in one method of making a mandrel embodying one form of the invention,

FIG. 5 is a diagrammatic elevation showing a step subsequent to that of FIG. 4, and

FIG. 6 is a section similar to FIG. 4 showing a step subsequent to that of FIG. 5.

In the drawings 10 designates a mandrel tube closed at its lower end by a foot plate 12 and closed at its upper end by a head plate or driving plate 14 which is struck by the driving hammer. The mandrel is of the solid core type, by which I mean that the cross section of the tube is a complete integral annulus. It may have a range of wall thickness from approximately an inch and a quarter to about an inch and three quarters. At suitable intervals along its length, for example at about four foot intervals, elongated openings or slits 16 are formed in any suitable manner as by burning with a cutting torch. The openings have rounded ends 18. Preferably wherever an opening occurs, there are four such openings distributed at 90 about the circumference of the tube. A gripping and driving connection for the shell to be driven is placed in each opening 16. This is in the form of a plug 20 provided on its outside surface with a number of slanting lugs 22 which conform to the spacing and pitch of the corrugations of the shell in which the mandrel is to be used. Each plug has rounded ends conforming to the shape of the slit 16 and has a snug but easily sliding fit in the opening. The plugs are expressed into the position providing a gripping and driving connection between tube and shell by 'eXpansible hoses inflated with compressed air, and are retracted by springs when the hoses are exhausted or deflated as will be explained.

As shown in FIG. 2 each plug 20 is attached to a flat retaining and bearing plate 24 by a pair of bolts 26 threaded into nuts 28 welded to the plate. The plate 24 is longer than the opening 16 and is slightly narrower than the width of the opening so that it can be inserted through the opening into the interior of the mandrel and placed approximately parallel to the axis of the tube 10. A retracting spring 30, between each end of the plate 24 and the tube, urges the plug 20 inwardly. The plate may be flat and the springs 30 may be leaf springs attached in any suitable manner but I prefer to form the plate and both springs as a single integral spring, having its ends reversely bent to form the springs 30 as shown in FIG. 1. In such case the spring plate 24 may normally (or when not stressed) be bowed or concave with respect to the tube 10, as indicated schematically by dotted lines in FIG. 1. This arrangement is preferred, for the retracting force can be provided principally by the main body of the spring between its recurved ends. The ends 30, while exerting some retracting force as springs, also act as slides for the end-s of the spring in flexing from its concave, retracted position to its flat position which holds the plug in shell-engaging position. Each spring 24 urges its plug 20 inwardly and the spring is calibrated so that in its relaxed position the ends of the lugs or cleats 22 do not protrude beyond the external diameter of the tube 10.

The lugs are expressed into contact with the shell by air pressure in an inflatable or expansible hose 32 which is supported and confined in a chamber or cage formed by a U-shaped channel member 34 extending substantially the entire length of the tube 10 and welded to the inside of the tube. Both edges of the channel member 34 are welded to the tube at least along lines or lengths which are adjacent both ends of each opening 16. I prefer to weld the channel members to the tube along their entire length.

As shown in FIGS. 1 and 3 at the upper end of the mandrel each channel member 34 is cut away as at 36 to receive an annular channel iron 38 the edges of which are welded to the inside of the tube 10 around its entire circumference. The chamber 40 confined between the tube 10 and the channel 38 provides a manifold for delivering air pressure from a .pipe connection 42 to the four hoses 32, each of which is closed at its ends, as indicated at 44 in FIG. 1 to form a fluid pressure chamber for operating the plugs. Each hose is connected to the manifold chamber 38 near its upper end but between its ends by a hollow nipple 46. By this construction the interior of the mandrel is entirely free of all unattached heavy structure, the only thing loosely attached to it being the four hoses which are of relatively low inertia. Each channel 34, being welded to the tube throughout its entire length, is an integral part of the tube and cannot move with respect to the tube when the hammer strikes the head plate 14. The cross section of each hose when inflated is so related to the cross section of the channel chamber, and the modulus of expansion, if any, of the hose is so related to the force of each spring that when the hose is inflated to drive a pile shell the hose substantially fills the channel. Also the hose is held by air pressure firmly in contact with all four sides of the channel chamber, except possibly in the corners, to provide four firm friction supports for the hose along its entire length. The only solid connection between the hose and the mandrel is at the nipple 46. Since the hose is of relatively low inertia and since the entire length of the hose is firmly supported against the channel iron 34 and the inside of the tube 10, the inertia effects which would tend to cause any relative movement between the hose and the nipple are so low that they can be absorbed by resilience of the hose and by the nipple without rupturing or damaging the air connection.

A feature of the invention is the construction of the mandrel so that the entire length of each hose supporting cage or channel can be welded to the mandrel tube 10. In this the relative length and diameter of the mandrel are critical. A single mandrel may be as much as 60 feet long. It will in general be not less than 8 feet long. It will have a maximum inside diameter of about 13 /2 inches and this dimension may be as little as 8 /2 inches. Welding of the channel to the tube must be done by welding apparatus, such as a torch or electrode, inserted from the ends of the tube. It is impossible, or at least impractical, to weld the entire length of a channel to the inside of such a tube 60 feet long or even 8 feet long. Consequently I build the mandrel either as indicated generally in FIG. 1, or as shown specifically in FIGS. 4 to 6. A length of the tubing designated in FIG. 1 which may be about four feet long is provided with the appropriate four circumferentially distributed slots 16 and lengths of channel 34 just equal to the length of the section 50 may be welded in place. For an 8 /2 inch (inside diameter) tube I prefer to make the sections about ,four feet long as this is the greatest practical length along which a section of channel can be welded from opposite ends along its entire length. Both ends of the section 50 and the channels may be finished flat and perpendicular to the axis of the tube and the desired number of such four foot lengths is then joined by welding as indicated at 52 in FIG. 1. This can be done effectively and inexpensively on an automatic welding machine using a shielded arc. This welding process provides a straight tube of any desired practical length, for example up to feet, which is smooth on the outside. Each channel 34, which runs the length of the tube, is made of a series of short channel members, butted end to end in alignment. The only openings needed are the oval or elongated plug openings 16 and the four threaded openings 54 for insertion of the nipples 46. The last or top section 50 contains the manifold ring 38.

Preferably the mandrel is assembled as shown more specifically in FIGS. 4 to 6.

First a tube 10, which may be four feet long having its plug openings 16 near one end, is assembled with four channel members 34, each also four feet long. The channels are welded to the tube with one end of each set back from the end of the tube near which are the plug openings 16. The other end of each channel protrudes from the other end of the tube a corresponding distance, for example about six inches as shown in FTG. 4. A plurality of such tube and channel assemblies are then assembled by inserting the protruding channel ends of one into the recessed end of the other as shown in FIG. 5. The channels are aligned, the tubes and channels abutted and the tubes welded on the outside as described in connection with FIG. 1. Thereafter a welding torch or electrode is inserted through the plug openings 16 as shown in FIG. 6 to weld the ends of the channel protruding from one tube to the recessed end of the adjacent tube, or to weld the abutted ends of the channels together, or both.

The hoses 32 are inserted. in the channels from one end. This can be readily done as the hoses are then deflated and there is clearance in the channels to receive them. The nipples 46, having previously been inserted in the hoses through the holes 54, are secured to the manifold by nuts 56 and packing washers 58, set by a wrench inserted through one of the openings 54. Three openings 54- are closed by flush plugs 60 and the air connection 42 is secured in the fourth opening 54. Then each spring 24 is inserted endwise through an opening 16 and held in place. The individual plugs 20 can then be attached to the nuts 28 by the bolts 26. Thereafter the foot plate 12 and head plate 14 can be attached and the mandrel is complete.

When the mandrel is to be lowered into a shell the hoses are deflated by exahusting the air pressure through the connection 42 so that the springs can assume their relaxed positions indicated in dotted lines as in FIG. 1 and retract the plugs 26 to bring the lugs 22 within the outer diameter of the tube. When the mandrel is in place in the shell the hoses are expanded to hold the plugs in the position shown in FIG. 1 in which the lugs 22 engage the corrugations of the shell establishing a firm driving connection between the mandrel and the shell. Upon completion of the driving the air pressure is exhausted, the springs retract the plugs to clear the shell and the mandrel is withdrawn by any suitable hoisting connection, not shown, as known in the art.

The entire structure is much lighter than a mandrel having guts shown in my patent referred to, and the inertia of the mandrel is correspondingly lower. This enables more of the energy of the hammer to be transmitted to the shell being driven, than with previously known m-andrels.

It is to be understood that the invention may be carried out or practiced in various ways other than the illustrative embodiment described herein and that the terminology employed is illustrative only and does not limit the invention.

I claim:

1. A pile driving mandrel comprising in combination a tube whose length is at least six times its internal diameter, a plurality of axially extending rows of axially elongated slits through the wall of the tube, said rows being distributed circumferentially about the tube, a plurality of channel members in the tube extending substantially the length of the tube, each channel member overlying one row of slits, each channel member being integrally joined to the tube at points adjacent each end of each slit to form an elongated first chamber overlying the row of slits, an elongated retaining plate associated with each slit and disposed within the tube, each plate being longer than its associated slit and insertable through the associated slit into the chamber, a shell gripping plug movable radially in each slit for engaging a shell outside the tube, each plug being secured to a plate, spring means adjacent the ends of each plate engaging the inner side of the tube for urging the associated plug inward, an elongated flexible and expansible fluid pressure chamber in each first chamber radially inward of said plates and extending throughout the length of the row of plates, a pressure fluid manifold integrally joined to the inside of the tube be tween the ends of the group of first chambers, said manifold passing through said first chambers and being pneumatically isolated therefrom, a pressure fluid transmitting connection between each pressure fluid chamber and the manifold within one of said first chambers, and means for supplying the manifold with pressure fluid to urge all of the plugs outward.

2. A pile driving mandrel comprising in combination a tube whose length is at least six times its internal diameter, an axially extending row of axially elongated slits through the wall of the tube, channel means in the tube extending substantially the length of the tube and overlying the row of slits, the channel means being integrally joined to the tube at points adjacent each end of each slit to form an elongated first chamber overlying the row of slits, an elongated retaining plate associated with each slit and disposed within the tube, each plate being longer than its associated slit and insertable through the slit into the chamber, a shell gripping plug movable radially in each slit for engaging a shell outside the tube, each plug being secured to a plate, spring means adjacent the ends of each plate engaging the inner side of the tube for urging the associated plug inward, an elongated flexible and expansible fluid pressure chamber in the first chamber radially inward of said plates and extending throughout the length of the row of plates, and an air-transmitting connection between the wall of the tub-e and the fluid pressure chamber for supplying the flexible chamber with pressure fluid to urge all of the plugs radially outward, the cross section of the fluid pressure chamber and its modulus of expansion being so related to the cross section of the first chamber and the force of the inwardly urging means respectively, that when the plugs are in their maximum outward position the cross section of the fluid pressure chamber substantially fills the cross section of the first chamber to provide substantially complete peripheral friction support of the fluid pressure chamber by the walls of the first chamber to reduce the inertia force of the fluid pressure chamber on said connection when the tube is struck by a driving hammer.

3. A pile driving mandrel comprising in combination a tube whose length is at least six times its internal diameter, an axially extending row of axially elongated slits through the wall of the tube, channel means in the tube extending substantially the length of the tube and overlying the row of slits, the channel means being integrally joined to the tube at points adjacent each end of each slit to form an elongated first chamber overlying the row of slits, an elongated retaining plate associated with each slit and disposed within the tube, each plate being longer than its associated slit and insertable through the associated slit into the chamber, a shell gripping plug movable radially in each slit for engaging a shell outside the tube, each plug being secured to a plate, springs means adjacent the ends of each plate engaging the inner side of the tube for urging the associated plug inward, an elongated flexible and expansible fluid pressure chamber in the first chamber radially inward of said plates and extending throughout the length of the row of plates, and means for supplying the flexible chamber with pressure fluid to urge all of the plugs radially outward, the cross section of the fluid pressure chamber and its modulus of expansion being so related to the cross section of the first chamber and the force of the inwar 1y urging means, respectively, that when the plugs are in their maximum outward position the cross section of the fluid pressure chamber substantially fills the cross section of the first chamber to provide substantially complete peripheral friction support of the fluid pressure chamber by the walls of the first chamber.

4. A pile driving mandrel comprising in combination a tube whose length is at least six times its internal diameter, a plurality of axially extending rows of axially elongated slits through the Wall of the tube, the rows being' distributed circumferentially about the tube, a plurality of channel means in the tube extending substantially the length of the tube, each channel means overlying one row of slits, each channel means being integrally joined to the tube at points adjacent each end of each slit in one row to form an elongated first chamber overlying the slits in one row, an elongated retaining plate associated with each slit and disposed within the tube, each plate being longer than its associated slit and insertable through the associated slit into the chamber, a shell-gripping plug movable radially in each slit for engaging a shell outside the tube, eaoh plug being secured to a plate, spring means adjacent the ends of each plate engaging the inner side of the tube for urging the associated plug inward, and an elongated flexible and expansible fluid pressure chamber in each first chamber radially inward of said plates and extending throughout the length of the row of plates, and means for simultaneously supplying the flexible chambers with pressure fluid to urge all of the plugs radially outward.

5. A pile driving mandrel comprising in combination a tube whose length is at least six times its internal diameter, an axially extending row of axially elongated slits through the wall of the tube, a channel member in the tube extending substantially the length of the tube and overlying the row of slits, the channel member being integrally joined to the tube throughout its length to form an elongated first chamber overlying the slits, an elongated retaining plate associated with each slit and disposed within the tube, each plate being longer than its associated slit and insertable through the associated slit into the chamber, a shell-gripping plug movable radially in each slit for engaging a shell outside the tube, each plug being secured to a plate, spring means adjacent the ends of each plate engaging the inner side of the tube for urging the associated plug inward, and an elongated flexible and expansible fluid pressure chamber in the first chamber radially inward of said plates and extending throughout the length of the row of plates, and means for supplying the flexible chamber with pressure fluid to urge all of the plugs radially outward.

6. A pile driving mandrel comprising in combination a tube Whose length is at least six times its internal diameter, an axially extending row of axially elongated slits through the wall of the tube, channel means in the tube extending substantially the length of the tube and overlying the row of slits, the channel means being integrally joined to the tube at points adjacent each end of each slit to form an elongated first chamber overlying the slits, an elongated retaining plate associated with each slit and disposed within the tube, each plate being longer than its associated slit and insertable through the associated slit into the chamber, a shell-gripping plug movable radially in each slit for engaging a shell outside the tube, each plug being secured to a plate, spring means adjacent the ends of each plate engaging the inner side of the tube for urgng the associated plug inward, and an elongated flexible and expansible fluid pressure chamber in the first chamber radially inward of said plates and extending throughout the length of the row of plates, and means for supplying the flexible chamber with pressure fluid to urge all of the plugs radially outward.

7. A pile driving mandrel comprising in combination an elongated tube having an axially elongated slit through its wall, a channel member in the tube extending throughout the length of the slit and beyond both ends of the slit, the channel member being integrally joined to the tube throughout its length to form an elongated chamber overlying the slit, an elongated retaining plate disposed within the shell, said plate being longer than the slit and insertable through the slit into the chamber and into a position overlying the slit, a shell-gripping plug movable radially in the slit for engaging a shell outside the tube, the plug being secured to the plate, spring means adjacent the ends of the plate engaging the inner side of the tube for urging 8 the plug radially inward, an elongated flexible and erpansible fluid pressure chamber in the first mentioned chamber radially inward of the plate, and means for supplying the fluid pressure chamber with pressure fiuid to urge the plug radially outward.

8. A pile driving mandrel comprising in combination an elongated tube having an axially elongated slit through its wall, a channel member in the tube extending throughout the length of the slit and beyond both ends of the slit, the channel member being integrally joined to the tube at points adjacent each end of the slit to form an elongated chamber overlying the slit, an elongated retaining plate disposed within the tube, said plate being longer than the slit and insertable through the slit into the chamber and into a position overlying the slit, a shell-gripping plug movable radially in the slit for engaging a shell outside the tube, the plug being secured to the plate, spring means adjacent the ends of the plate engaging the inner side of the tube for urging the plug radially inward, an elongated flexible and expansible fluid pressure chamber in the first mentioned chamber radially inward of the plate, and means for supplying the fluid pressure chamber with pressure fluid to urge the plug radially outward.

9. A pile driving mandrel comprising in combination an elongated tube having an axially elongated slit through its wall, an elongated normally bowed spring longer than the slit and insertable through the slit into the tube into a position generally parallel to the axis of the tube and overlying the slit, a shell-gripping plug secured to the spring and movable radially in the slit for engaging a shell outside the tube, the wall of the tube being engaged beyond the ends of the slit by the spring near its ends and the spring being biased for urging the plug radially inward, and a plug operator in the tube for overcoming the force of the spring and urging the plug radially outward.

10. A pile driving mandrel comprising in combination an elongated tube having an axially elongated slit through its wall, an elongated retaining plate disposed within the shell, said plate being longer than the slit and insertable through the slit into the tube into a position generally parallel to the axis of the tube and overlying the slit, a shell-gripping plug secured to the plate and movable radially in the slit for engaging a shell outside the tube, springs formed integral with the plate and disposed between the ends of the plate and the wall of the tube beyond the ends of the slit for urging the plug radially inward, and a plug operator in the tube for overcoming the force of the springs and urging the plate and the plug secured thereto radially outward.

11. A pile driving mandrel comprising in combination an elongated tube having an axially elongated slit through its wall, an elongated retaining plate disposed within the shell, said plate being longer than the slit and insertable through the slit into the tube into a position generally parallel to the axis of the tube and overlying the slit, a shell-gripping plug removably secured to the plate and movable radially in the slit for engaging a shell outside the tube, springs between the ends of the plate and the wall of the tube beyond the ends of the slit for urging the plug radially inward, and a plug operator in the tube for overcoming the force of the springs and urging the plate and the plug secured thereto radially outward.

12. The method of making a pile-driving mandrel which consists of forming in a short length of tube an opening elongate in the axial direction of the tube, placing a channel member whose length is substantially equal to the length of the tube inside the tube to form a chamber into which said opening provides access, welding the channel member to the inside of the tube throughout a major portion of the length of the channel member, abutting a plurality of lengths of tubes with channel members so welded therein in end to end relationship with the channel members in alignment and in abutment, welding the tube sections together from the outside and then welding the channel members together by means of a welding tool inserted through the openings to form a mandrel having a smooth outside surface and having a smooth continuous hose supporting chamber on its inside surface integral with the tube, inserting a hose into the hose supporting chamber to form the expansible chamber, inserting plates through the openings between the hose and the tube in abutting relationship with the hose,

inserting plugs in the openings and securing the plugs to 10 the plates.

References Cited by the Examiner UNITED STATES PATENTS CHARLES E. OCONNELL, Primary Examiner.

JACOB SHAPIRO, Examiner. 

1. A PILE DRIVING MANDREL COMPRISNG IN COMBINATION A TUBE WHOSE LENGTH IS AT LEAST SIX TIMES ITS TERMINAL DIAMETER, A PLURALITY OF AXIALLY EXTENDING ROWS OF AXIALLY ELONGATED SLITS THROUGH THE WALL OF THE TUBE, SAID ROWS BEING DISTRIBUTED CIRCUMFERENTIALLY ABOUT THE TUBE, A PLURALITY OF CHANNEL MEMBERS IN THE TUBE EXTENDING SUBSTANTIALLY THE LENGTH OF THE TUBE, EACH CHANNEL MEMBER OVERLYING ONE ROW OF SLITS, EACH CHANNEL MEMBER BEING INTEGRALLY JOINED TO THE TUBE AT POINTS ADJACENT EACH END OF EACH SLIT TO FORM AN ELONGATED FIRST CHAMBER OVERLYING THE ROW OF SLITS, AN ELONGATED RETAINING PLATE ASSOCIATED WITH EACH SLIT AND DISPOSED WITHIN THE TUBE, EACH PLATE BEING LONGER THAN ITS ASSOCIATED SLIT AND INSERTABLE THROUGH THE ASSOCIATED SLIT INTO THE CHAMBER, A SHELL GRIPPING PLUG MOVABLE RADIALLY IN EACH SLIT FOR ENGAGING A SHELL OUTSDIE THE TUBE, EACH PLUG BEING SECURED TO A PLATE, SPRING MEANS ADJACENT THE ENDS OF EACH PLATE ENGAGING THE INNER SIDE OF THE TUBE FOR URGING THE ASSOCIATED PLUG INWARD, AN ELONGATED FLEXIBLE AND EXPANSIBLE FLUID PRESSURE CHAMBER IN EACH FIRST CHAMBE RADIALLY INWARD OF SAID PLATES AND EXTENDING THROUGHOUT THE LENGTH OF THE ROW OF PLATES, A PRESSURE FLUID MANIFOLD INTEGRALLY JOINED TO THE INSIDE OF THE TUBE BETWEEN THE ENDS OF THE GROUP OF FIRST CHAMBERS, SAID MANIFOLD PASSING THROUGH SAID FIRST CHAMBERS AND BEING PNEUMATICALLY ISOLATED THEREFROM, A PRESSURE FLUID TRANSMITTING CONNECTION BETWEEN EACH PRESSURE FLUID CHAMBER AND THE MANIFOLD WITHIN ONE OF SAID FIRST CHAMBERS, AND MEANS FOR SUPPLYING THE MANIFOLD WITH PRESSURE FLUID TO URGE ALL OF THE PLUGS OUTWARD. 